Use of optically readable legends or labels such as bar codes on products to record and track the products is widely practised in industry and commerce. It is becoming common for bar code scanner devices which are used to read bar codes, such devices being herein referred to as ‘imagers’, to be worn on the hand of a user to provide a more ergonomically satisfactory and natural operation for the user. Also with the development of low power, short-range radio data transmission standards such as that known in the industry as Bluetooth™, it is not necessary to have a wired connection from the imager to the equipment processing and using the barcode or image data.
The use of CMOS imager chips in imagers is also becoming more popular because of their lower power consumption (as compared, for example to laser bar-code imagers), allowing a much smaller power source to be used. For example, the Motorola MCM20014 VGA resolution ImageMOS™ sensor can capture an image in 1/30th second whilst consuming 70 mA at 3.3V whereas a conventional laser scan engine imager will take 1/20th second and require 150 mA at 5V. An imager chip requires, however, an additional light source to illuminate the target area, e.g. the area on a product where a barcode is provided, if the ambient background light is not sufficient, whereas a laser scanner imager is its own light source. The additional light source is normally provided by a number of LEDs (Light Emitting Diodes or forward biased semiconductor p-n junction diodes) incorporated in a unit which also provides the reader function. The power consumption of the additional light source is considerable and causes the overall imager power consumption to be raised typically to 120 mA at 5V. This is nearly the same as that for the laser scanner imager.
In some proposed scanning and LED illuminating imager devices, an attempt has been made to increase the amount of ambient light on the target by employing light collection and guidance, for example as described in U.S. Pat. No. 6,042,012 but such optical collection systems add considerably to the size and weight of the imager and so are not suitable for use in wearable scanner applications.
Other proposed imagers use a targeting light spot or frame to ensure that the illuminating light source is aligned on the target before scanning so reducing the total illumination time and therefore the energy consumption, as for example described in U.S. Pat. No. 6,340,114. However, again the necessary optical system unfortunately adds considerably to the size of the imager.
In summary, prior art imagers also incorporating an illuminating device are bulky and relatively heavy and are not particularly suitable for hand carried operation.